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212                    METALLURGY OF CAST IRON.
With charcoal iron castings we can have low silicon without much sulphur, whereas with coke and. anthracite iron castings, if we have low silicon, we may generally expect high sulphur. Charcoal pig metal being the most free from sulphur and impurities, the softest strong castings are obtained from it, especially when melted in an air furnace. Sulphur is very deceptive in pig metal. It can lurk in hiding so as to be present to a much greater degree than the eye of an expert can suspect. For this reason chemical analysis is very essential in order to ferret it out. Sulphur can cause iron to be red short, as well as cold short.
Two points of sulphur are more effective in changing the character of iron than ten to fifteen points of any other constituent which iron possesses. Its influence in so greatly changing the character of iron is due to its ability to radically increase the percentage of combined carbon in iron. The alteration that a few points in sulphur can effect in the " grade " of iron is often surprising, and for this reason founders should be most watchful of sulphur. The amount of sulphur in pig metal generally ranges from .01 for No. i iron tip to .10 for ''white iron." For No. i pig metal it rarely exceeds 0.03; Nos. 3 to 4, 0.05, and for white pig iron Sulphur in iron can cause excessive shrinkage as well as contraction, the former often being the cause for shrink holes and the latter for cracks in castings.*
Manganese, when increasing the combined carbon, will deepen the chill and cause greater shrinkage and contraction, and to a limit greatly strengthens iron.
*For an article on the effects of sulphur in strengthening iron, sec Chapter XLIII.their 3.00 to 4.00 per cent, silicon irons, as a little goes a long ways and often prevents shutting down for the want of regular irons.
he now can about moulding sand, ramming, venting, Steel Co., Vale University. & Sons, Hecla Works, England; R. C. Hindiey, M. Hoskins, Harvard College, Havemeyer University, Henry Hiels Chemical Co., Isabella Furnace, Iron Gate Furnace, Iroquois Iron Co., Illinois Steel Co., Jefferson Iron Co., Kittan-ning Iron & Steel Co., C. A. Kelly Plow Co., Lebanon Furnace, Longdale Iron Co., Lackawanna Iron & Steel Co., Logan Iron........................   16,720     "                                     t-